Tank



July 5, 1932. v H, c. BOARDMAN l865822 TANK y Filed Jan. 10, 1931 5 Shee'f.s-Sheel'l l RG i Qywemg July 5, 1932. H. c. BARDMAN 1,865,822

TANK

Filed Jan. l0. 1951 5 Sheets-Sheet 2 Patented July `5, 1932 UNITED `STATES PATENT OFFICE EARRY C. BOARDMAN, F CHICAGO, ILLINOIS, ASSIG'NOB T0 CHICAGO BRIDGE & IRON COMPANY, 0F CHICAGO, ILLINOIS, A. CORPORATION 0F ILLINOIS TANK Application led January 10, 1931. Serial No. 507,985.

made hemi-sph'erical and hemi-ellipsoidal in* shape. In the latter case, an additional sup- 1,5 p ort has frequently been provided at the center by a riser pipe, or otherwise.

The principal feature of my invention is the provision of a bottom for the kind of tank described, so curved that it will be subi Y stantially equally stressed throughout its area. This will permit the use of metal of substantially uniform thickness in a bottom of this kind which is suspended by its edgel or edges. Obviously, when the tank is full if of liquid, the pressures on points in the bottom at different' heights will be different because of the different heads of liquid and tensional stresses due to the support of the bottom by the edge or edges. Owing'to the 3 particular curvature employed, however, the maximum stresses at all points in the bottom will be substantially uniform.v

Other features and advantagesof my invention will appear more fully as vI proceed 3f with my specification.

In those forms of devices embodying the features of my invention shown in the ac companying drawingsy r Figure 1 is a view partly in side elevation and partly in section of an elevated tank with a suspended bottom supported, only at its outer edge; Fig. 2 is adiagrammatic view showing the method of obtaining the curvature of the bottom; Fig. 3 is a view similar u to Fig. 1, showing a bottom suspended at land simplicity in cost and manufacture.

its outer edge and also at its inner edge by the provision of a centrally arranged riser pipe; Fig. 4 is a diagrammatic view showing the method of obtaining the curvature of the bottom of the tank of Fig. 3; and 50 Fig. 5 is a view similar to Fig. 4, showing a modification. y

The tank shown in Fig. 1 has a cylindrical body portion supported on posts 11. The bottom 12 is preferably made of sheet metal and so curved that the maximum stresses at all points are substantially uniform. This permits the use of metal of substantially uniform thickness, thus making for economy I shall now describe in detail the method of'determining the curvature of the bottom 12 to achieve the objects of the invention as above set forth. It will be seen that the tank is a solid of revolution about a vertical central axis and that all diametrical sections of the bottom are similar. It will be necessary, therefore, to obtain only .the curvature of such a section. f

Fig. 2 represents the curve of a diametrical section of the bottom 12. This curve is obtained as follows. CL represents the eenter line of the tank. B is the low pointon the bottom. C is the maximum height of water. 1'1 represents the radius of curvature in a plane perpendicular to the drawing or paper through a line normal to the surface of the bottom. r2 represents the radius of curvature in the plane of the drawing or paper through a line normal to the surface of the bottom. T 80 represents the tension or stress and P the pressure.

For the purpose of illustration, I 'shall show the method applied to a water tank with a diameter of substantially 40 feet and a total height of substantially 40 feet from the low point in the bottom to the upper edge of the cylindrical body portion or shell. That is the. distance BC is 40 feet. In the practice of the invention, it maybe necessary to resort to experimentation or the trial and error method to determine the curve and thickness of metal for tanks of certain desired capacities and dimensions. In the case given, it Will be assumed that the permissible tension in the bottom plates is 31,500 pounds per linear foot. This may have been obtained, for example, on the assumption that 1% sheets will be used, designed for a stress of 10,000 pounds per square inch. In order to obtain a factor ofsafety, or allowing for weakness in joints, the plates may be rated at This makes the permissible stress 10,000 x 3/8 x .70, which equals 2,620 pounds per linear inch or 31,500 pounds per linear foot. It will be seen hereinafter, however, that all that is necessary is to know the permissible stress. The curvature can then be ascertained. The permissible stress in any material to be used may be computed in any desired manner.

Assuming, in the case given, that T equals 31,500 and that the tank is 40 feet high, r1 and r2 can be found at all points in the following manner. Commencing at B, it is known that a 40 foot head of water will exert a pressure of approximately 40 x 62.5 pounds lor 2500 pounds. It is also known that at any point on the bottom This is obtained from the equation Trl Tra Prlr,

PTlTg'- T72: Tf1

72(1) f1 .T) Tf1 The ' the maximum water line CW.

T72 TVM-T Using the assumed data, r2 at B is obtained as follows:

=25.2 -feet It will be seen that if the assumed tension is smaller, r2 will be shorter. If the assumed permissible tension is too small, r2 will be so short that the bottom curve, if plotted as hereinafter described, will not reach the side of the body cylindrical portion. Consequently, the-permissible tension must be great enough so that r2 will be long enough at B so that the curve when plotted, will connect with the cylindrical body portion of the tank. eater the assumed tension, the longer r2 wi l be and the flatter the bottom will be. With lesser assumed tensions, the bottom will be more curved. As stated, however, the curve must be fiat enough so that the bottom will join the sides of a cylindrical body portion of the diameter desired.

' This distance may then be measured vertically on the line CL, giving the center D, the distance D-B being 25.2 feet. With the center D and radius DB, the arc BE is then drawn. At E, the pressure will beless than at B because of the reduced head. This head at E may be measured vertically from E to Assuming this distance to measure 38.4 feet, P at E will be 2400. `It will be seen, therefore, that r2,

as taken 'for B, will notbeccorrect at E. The

correct r2, however, at E can be obtained by using the equation: f

P fx

4.LCE

distance trom the point inV question along r2 from the point 'to where r2 intersects the center line CL. At E, therefore:

A new center ma then be formed by extending the line E to F, the distance E F being 27.4, which is the new r2.

With this new radius 27.4 and using the center F, another arc E G is drawn and a new r2 obtained at this point. At G, r1 is the distance along G F from G to the point where G F intersects the line C L at H. The distance G H can be measured and it will be assumed that this distance is 26 feet. This gives r1 at G as 26 feet. The head at G can 27.4 feet.

also be measured and the pressure obtained.

Assuming that the vertical distance from G to the line C W measures 36 feet, P at G will be 2250. A new and correct 7:2 at G can then be formed as follows:

-Y 31.500 At G 2: 31500 22m-2,5-

The new r2 or 34.6, can then be measured =30. 3 feet.

alongtheline K M extended to the point N.

R is taken as 80 feet.

" center.

N is then the new 1'2 atK and with this radius, the arc K P is drawn with N as a In this manner, the curve is continued until the side W P of the tank is reached. As here shown, the diameter W R is taken as 40 feet. Obviously, any desired diameter may be taken and the curve continued until the side is reached. By taking more and shorter arcs, greater accuracy is obtained.

In Figs. 3 and 4, I have shown a bottom suspended by its outer edge, which is attached vto the cylindrical body portion and also by its inner edge which is attached to the upper edge of the central riser pipe S which acts as a support. The curve for this bottom is shown 1n Fi 4 and the method of producing it is substantlally the same as above described. As here shown, C L represents the center line of the tank. In this case, the diameter W B is the lowest point in the bottom and corresponds to B in Fig. 2. It is assumed that 3/8 lmetal is used as above described and that the permissible tensure at B is 50 x 62.5 or 3125.

vwhere it intersects C L at M.

sion or stress 31,500 pounds, as computed above. The desired diameter of the riser pipe is also taken arbitrarily and here this is assumed to be S T.` The maximum desired water depth is also arbitrarily taken and this is assumed to be 50 feet, which is the vertical distance from the line X Y to the line W R.

The point B is arbitrarily chosen .somewhere on the line X Y, preferably about midway between X and Y, or somewhat nearer Y. By trial or experiment, the permissible tension must be great enough so that the radii (r2) will be long enough so that the curve will be flat enough to reach the side wall W V and the riser at S at the desired heights. If the 1'2 radii are too short, the bottom curve will not connect with the shell or riser or will connect at points which are higher than desired. By increasing the permissible tension, however, the bottom may be made as flat as desired.

Assuming the point B in Fig, 4 to be located as above described, the curve from B to V is made substantially as described in connection with Fig. 2. That is, as follows. The permissible tension is 31,500. The presrl at B is ininity. Therefore, by the equation given above:

With the radius 1'2 as 10 and D as a center, the arc B E is drawn. At E', the height `can be measured from E to the line W R.

At Ek, ,FM 3000 31500 A new center is then found by extending the line E D to F', the distance E F being 13.8 feet. v

= 13.8 feet.

With thisnnew radius 13.8 feet and using the center F', another arc E G is drawn and a new r2 similarly obtained atthis point. At G', 1'1 is the distance along G F extended to Assume this to vmeasure 45 feet. Assume the head of water at G to measure 44.8 feet, the pressure at G will be 2800. Therefore,

A new center is obtained by measuring 15 J With the center J', the arc G K is drawn. At K', r1 will be the distance K N.

Measuring this along the line K' J' from K' gives the new center at N". With this new center, the arc K' V is drawn. This brings the curve into the side ofthe cylindrical body portion.

The curve B S is obtained in a similar manner, except that r1 becomes minus so that With the center D', the arc B' E" is drawn. At this point, r1 is the line E H", which is the extension of the line D E" to where it intersects C L at H". Assume that this measures 43 feet and that the pressure at E" is 3000 pounds.

At E", T2:

=8.4 feet.

Measuring 8.4 feet from E" gives the new center F. Using this, the arc E" G" is drawn.

1-1 at G" isthe distance G" M". Assume this to measure 26 feet.

r, at G= =7.9 feet.

This requires that the center for the first r2 be taken on the horizontal line V V'. In such case r1 at V will be the radius of the tank which is assumed to be 40 feet. Assume that it is desired that the cylindrical body portion be 30 feet high so that the Water head at V will be 30 feet.

The rad`ius 29 feet is then used with the center 100 to draw the arc V K". At K" a new r2 may be computed as follows. At K", r1 equals the distance K N'". Assume the pressure at K" to measure 2390 pounds. Assume K N'" to measure 40.2.

At KH, 1- ML =19.6 feet. 2390 31500 Measuring the distance 19.6 feet from K gives the new center 101. With this center, the arc K" 102 is drawn. 1'1 at 102 is 102-*103, which measures 45 feet. Assume the pressure at 102 to be 2800 poun is.

At T2:

= 12. 7 feet'.

This gives the new center 105 and the arc 104-106 is drawn until the radius becomes vertical which must be the lowest point of the bottom. At the'point 106, 1'1 is innity. As-

sume the pressure to measure 3125 pounds at i At 106, r2= 31500 Measuring 10 feet vertically from 106 gives the new center 107.

The curve is similarly continued to the right of the vertical line through 106, except that in compiling T2, it is to be noted that r1 becomes minus. r2, therefore, equals With the radius 10, the arc 106-108 is drawn. At 108, r1 is the distance 108-109. Assume this measures 43 and that the pressure at 108 is 3000.

= 8.4 feet.

Using the distance 8.4 feet, the center 110 is obtained for the new r2 at 108 and the arc V108-111 drawn. Y

If the pressure at 111 is 2800 and the distance 111--112 measures 26, then 31500 m feet.

This distance gives thel new center 11i) and the arc 113-114 is drawn. It will be sven that rzlat 111= at 114, the arc becomes vertical and, therefore, the curve must be stopped there and the riser pipe 115 made of sufficient diameter to support the inner edge of the bottom at that point.

any point desired and the riser pipe attached. P

In the curve shown in Fig. 4, the data taken were similar to those used in F ig. 5 and, consequently, the curve at V and S comes into the shell and riser, respectively, substantially on a tangent. Obviously, however, in this case, if heavier bottom plates were used with a greater value of T, the curve would be Hatter and the bottom would come into the shell at V not on a tangent, but more as the bottom joins the shell at P in Fig. 2. Likewise, the,

curve would not meet the riser pipe at S as a tangent, but at a larger angle.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications.A Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of my invention as disclosed in the appended claims, in which it is my intention to claim all novelty inherent in my invention as broadly as permissible, in view of the prior art.

What I regard as new, and desire to secure by Letters Patent, is:

1. A tank of the character described with a substantially cylindrical body portion having a curved sheet mtal bottom with a central opening, said bottom being suspended partly by its outer edge and partly by its inner edge surrounding said opening, said bottom being so shaped that a diametrical vertical section deines two similar curves in each of which the successive radii from the lowest bottom point to the outer edge are successively longer and from the lowest point to the inner edge are successively shorter.

V2. A tank of the character described with a substantially cylindrical body portion having a curved sheet metal bottom with a central opening, said bottom being suspended partly by its outer edge and partly byv its inner edge surrounding said opening, said bottom being so shaped that a diametrical vertical section defines two similar curves in each of which the successive radii from the lowest bottom point to the outer edge are successively longer and from the lowest point to the inner edge are successively shorter and in which such radius at each point is shorter v the plane of the section and passing through a line normal to the surface at such point.

3. A tank of the character described with a substantially cylindrical body portion having a curved sheet metal bottom with a central opening, said bottom being suspended" partly by its outer edge and partly by inner edge surrounding said opening, sald Ibottom being so shaped that a diametrical vertical section defines two similar curves in each of which the radius at each point is shorter than the radius in a plane at right angles to the plane of the section and passing through a line normal to the surface. at such oint.

In Witness whereof, I have hereunto set my hand and seal, this third day of January,

HARRY C. BOARDMAN. 

